Chemical vapor deposition methods are employed to form films of material on substrates such as wafers or other surfaces during the manufacture or processing of semiconductors. In chemical vapor deposition, a chemical vapor deposition precursor, also known as a chemical vapor deposition chemical compound, is decomposed thermally, chemically, photochemically or by plasma activation, to form a thin film having a desired composition. For instance, a vapor phase chemical vapor deposition precursor can be contacted with a substrate that is heated to a temperature higher than the decomposition temperature of the precursor, to form a metal-containing film on the substrate. Preferably, chemical vapor deposition precursors are volatile, heat decomposable and capable of producing uniform films under chemical vapor deposition conditions.
The semiconductor industry is currently considering the use of thin films of various metals for a variety of applications. Many organometallic complexes have been evaluated as potential precursors for the formation of these thin films. A need exists in the industry for developing new compounds and for exploring their potential as chemical vapor deposition precursors for film depositions.
Tantalum nitride (TaN) materials are being considered for a number of applications in the electronics industry for next generation devices, including copper diffusion barrier and electrodes. The industry movement from physical vapor deposition to chemical vapor deposition and atomic layer deposition processes due to the increased demand for higher uniformity and conformality in thin films has lead to a demand for suitable precursors for future semiconductor materials.
TaN film between copper interconnect and dielectrics act a barrier which prevents copper diffuses into dielectrics. Currently the TaN barrier is deposited using physical vapor deposition (PVD) technology. However, for the future generation microelectronics, where the feature size will shrink to below 65 mn, the PVD technology may not be able to deposit ultra thin conformal film to meet the challenges. Atomic layer deposition (ALD) technology is superior to PVD technology in depositing thin film. However, the challenges for ALD technology is availability of suitable precursors. ALD deposition process involves a sequence of steps. The steps include 1) adsorption of precursors on the surface of substrate; 2) purging off the precursor molecules in gas phase; 3) introducing reactants to react with precursor on the substrate surface; and 4) purging off excess reactant.
For ALD processes, the precursor should meet stringent requirements. First, the ALD precursors should be able to form a monolayer on the substrate surface either through physisorption or chemisorption under the deposition conditions. Second, the adsorbed precursor should be stable enough to prevent premature decomposition on the surface to result in high impurity. Third, the adsorbed molecule should be reactive enough to interact with reactants to leave a pure phase of the desirable material on the surface at relatively low temperature.
Prior art TaN ALD precursors have one or more of following disadvantages: 1) solid state, 2) low vapor pressure, 3) wrong phase of the deposited material, and 4) high carbon incorporation in the film. Ta(NMe2)5 (PDMAT) is one of the prior art candidates but it is a solid. This precursor has also a tendency to form Ta3N5 instead of desired TaN. Ta3N5 is a insulator and a undesirable phase. Another prior art TaN precursor is t-BuN═Ta(NEt2)3 (TBTDET), which has low vapor pressure and often results in high carbon impurity in the film.
There are three types of prior art TaN precursors, namely TaCl5, Ta(NR2)5, R—N═Ta(NR2)3. TaCl5 is most inexpensive among the TaN precursors. However, TaCl5 is a solid and Cl incorporation in film is a serious problem. The chlorine is corrosive and will cause microelectronics device to malfunction. PDMAT does not have chloride in the composition therefore it does not have Cl incorporation problem. However, PDMAT is also a solid and has a tendency to form Ta3N5, which is dielectrics and is undesirable phase for barrier application. The third type of the TaN precursors is R—N═Ta(NR2)3 and the representative example is TBTDET. TBTDET is a volatile liquid and more favorable to form TaN phase. However, TBTDET have relatively low vapor pressure and the film deposited from TBTDET often has high carbon impurity.
In developing methods for forming thin films by chemical vapor deposition methods, a need continues to exist for chemical vapor deposition precursors that preferably are liquid at room temperature, have relatively high vapor pressure and can form uniform films. Therefore, a need continues to exist for developing new compounds and for exploring their potential as chemical vapor deposition precursors for film depositions. It would therefore be desirable in the art to provide a chemical vapor deposition precursor that is a liquid at room temperature, has a high vapor pressure and can form uniform films.